Docker platform

Docker is one of the most popular platforms that enable developers to host their applications within containers. It can be run on either the Windows, Linux, or macOS and ensures a standardized software deployment. The beauty of the system is that it allows local development on a container platform (such as Docker) and can be easily redeployed into the Azure cloud for sharing and distribution. The package will run as expected since all the package components are bundled into the Docker image you deploy. Docker acts as the container host as well as a tool for building containers. When containers are deployed through ACI, the service allows them to be scaled easily.

Docker terminology

When working with Docker and container instances, you should understand the following terminology. This will help you become comfortable working with containers and performing actions such as creating, building, and testing containers:

• Container: Thisrefers to an instance of one of your Docker images. As we discussed, containers are specialized packages of software that bundle application software with associated configuration files, libraries, and dependencies that are required to enable an application to run. In Docker, this consists of the Docker image, the execution environment, and your standard set of instructions. The platform enables you to create multiple instances of a container using the same image, which is important to remember when you want to scale your application.

• Container image: Thisrefers to all the dependencies and information packaged together that are required to create a container. These include frameworks, as well configurations for deployment and executions that a container runtime uses. An image is typically created from multiple base images stacked on top of each other to form the container’s filesystem. An image is immutable once it has been created.

• Docker Registry: This is therepository provided by the Docker platform for storing various image files. Azure has another solution, however— Azure Container Registry, which is the solution we will use.

• Build: This is the action of building your container. The buildwill be based on the container image and will be constructed based on the information provided by the Dockerfile. The build also includes any other necessary files.

• Pull: This refers to theaction of downloading a container image from one of your container registries.

• Push: Thisrefers to the action of uploading a container image to one of your container registries.

• Dockerfile: This defines instructions for building your image. It is stored as a text file. The first line in a Dockerfile structure is used to identify the base image needed, while the rest of the file contains the associated build actions for your image.

The Docker platform is structured as per the following diagram. You will notice the container registry comprises Azure Container Registry, Docker Hub, or another container registry, the Docker Engine components, and the containers. The following diagram will help you understand the relationship between these components:

Figure 11.5 – Docker components

You now understand more about the Docker platform, and you are now aware of the various components that work together to enable your solution. Next, we will explore how to set up Docker.